Witty Must Deal With Weak Sales, Bribery Allegations; Shares in Drug Maker Are Off 15%

LONDON—GlaxoSmithKline PLC Chief Executive Andrew Witty is under pressure. Weak sales, disappointing new-drug launches, a profit warning and bribery allegations have helped cause a 15% slump in the drug maker's shares this year, as those of its rivals have gained ground.

"I think the pressure on him has been building," said Société Générale analyst Stephen McGarry.